The term "phototherapy" relates to the therapeutic use of light, and the term "illuminator" refers to a device that is intended to be used externally to administer light to the skin for therapeutic purposes. Some phototherapy devices, in contrast, are provided on probes and are designed to be used internally.
External phototherapy has been shown effective in treating various medical conditions. For example, studies have shown that certain light spectra are effective in treating bulimia nervosa, herpes, psoriasis, seasonal affective disorder, sleep disorders, acne, skin cancer, and other conditions. One of the conditions most widely treated with phototherapy is hyperbilirubinemia in newborn infants, typified by an elevated level of a toxic molecule known as bilirubin in the infant's blood. During a natural process where the body scavenges iron from a substance known as "heme," bilirubin is produced. Normally, bilirubin is a conjugated within the liver and excreted. A fetus cannot conjugate bilirubin, however, so it is cleared via the placenta. During the initial neonatal period, the infant's liver may be too immature to conjugate bilirubin. If the condition remains untreated, the serum bilirubin levels may increase to the clinical condition of jaundice, since there is no effective excretory pathway. High levels of bilirubin in the neonate may cause irreversible brain damage and even death.
About 60 percent of newborns become clinically jaundiced at some time during the first week after birth. The proportion increases to 80 percent in premature infants. Consequently, hyperbilirubinemia is one of leading causes of hospital readmissions of newborns. Phototherapy is the treatment of choice for neonatal unconjugated hyperbilirubinemia, and has been used worldwide for decades with no known significant side effects. Phototherapy treats hyperbilirubinemia by changing bilirubin from its non-water-soluble form to water-soluble byproducts which can be bound to albumin, transported to the liver, and excreted.
As a yellowish pigment, bilirubin absorbs visible light in the blue, violet, and green spectra, and most readily absorbs wavelengths in the range of 400-500 nm, with a maximum absorption peak in the 450-460 nm range, i.e., blue light. Green light is also effective in phototherapy because light of longer wavelengths penetrates the skin more deeply. There is a dose-response relationship in the efficacy of phototherapy. That is, there is an increased response for higher doses of therapeutic light, as shown by a decrease in bilirubin levels.
Illuminators for phototherapy which are known in the art fall into two general categories: banks of light and fiber-optic illuminators. The earliest phototherapy illuminators included banks of light placed over an incubator, above an open bassinet, under a hood, or under a transparent support. Either fluorescent tubes or metal halide lamps typically serve as the light sources, although arrays of light-emitting diodes (LEDs) are also known in the art. These light sources are spaced from the infant and illuminate the whole body of the infant.
Illuminators using banks of light suffer from a number of drawbacks. The infant must wear sometimes uncomfortable eye protection during this treatment, either by using an appropriate shield or goggles, or even by taping the eyes shut, because the intense light can cause permanent eye damage. The relatively large size of the equipment takes up valuable free space in a typically cramped neonatal hospital ward. The banks of lights generate undesirable heat, and interfere with personnel attending to the patient. The heat generated is of vital concern in infant phototherapy. Newborn infants are extremely sensitive to heat, and it has been found that the heart rate of preterm infants increases significantly when the environmental temperature is raised as little as five degrees Celsius above normothermia. Hyperthermia has been associated with heart irregularities, heatstroke, and sudden infant death syndrome. Consequently, the infant's temperature must be frequently monitored when the infant is under a bank of phototherapy lights. Moreover, the relatively bulky equipment is not well-suited for home use, and thus the newborn infant must remain longer in the hospital.
Primarily in response to the desire of parents to bring their newborn infants home sooner, portable fiber-optic mats or wraps have been developed. These fiber-optic illuminators transmit light from a remote source through a fiber-optic cable to a flexible mat having a weave or other arrangement of optical fibers which can be worn next to the patient's skin. Because fiber-optic illuminators are placed around or under only a portion of the infant, its eyes are not exposed to intense light and eye protection is not necessary. Because the light source is remote from the flexible mat next to the patient, a filter can be used to attenuate any appreciable heating. Most importantly, since infant can be held and attended to while undergoing phototherapy treatment, fiber-optic illuminators promote better infant-parent bonding during the first few weeks of life. Commercial fiber-optic phototherapy illuminators include Ohmeda's BiliBlanket and Respironics'Wallaby II, which have tungsten halogen lamps and quartz halogen lamps, respectively, as their light sources.
FIG. 1 illustrates a fiber-optic mat type of illuminator of the prior art. The illuminator includes a woven fiber-optic mat 10 connected by a cable 12 to a housing 14 for a source of light. Alternatively, the mat may contain a plurality of fiber-optic strands which are cut or otherwise adapted to distribute light in a pinpoint pattern over the surface of the mat. The connector 16 is affixed to an end of the cable 12 and is inserted into the housing 14 to receive the light energy. The housing 14 includes the front face 24 on which may be mounted a power switch 20, a control indicator 22, and indicator lights 26 and 28. The mat 10 comprises a plurality of optical fibers woven so as to emit light energy for phototherapy.
Despite several advantages over radiant-type illuminators, fiber-optic illuminators are not ideal for several reasons. Significantly, fiber-optic illuminators typically deliver a lower overall amount of light than overhead banks of light, because the light is transmitted from a remote source to a relatively small fiber-optic mat. Moreover, to deliver even this limited amount of light, fiber-optic illuminators require a high-intensity light source such as halogen lamp, and an expensive optical filter to eliminate unwanted heat and ultraviolet light. Woven fiber-optic mats typically rely upon the geometry of the various emitting layers of fiber to control the level of light emittance. Since the patient is in direct contact with the fiber-optic mat, there is some pressure applied which may change the geometry, and thus change the level of light. In contrast, fiber-optic mats using a plurality of cut strands to distribute light are often thicker near the light source where the strands originate than at the other end of the mat. In either case, the light intensity may be more concentrated near the light source than at the other end of the mat.
Recently, researchers at Stanford University have studied the efficacy of high-intensity light-emitting diodes (LEDs) for phototherapy of hyperbilirubinemic neonates. The in vitro photodegradation of bilirubin in human serum albumin from both LEDs and conventional light sources was measured, with the conclusion that LEDs are more effective. The use of LEDs for use in home phototherapy devices was mentioned. However, no specific device structure was disclosed, nor was any consideration given for the safety and comfort of the patient, for example a newborn infant, undergoing phototherapy.
Several hurdles remain to the use of LEDs in home phototherapy devices. Problems related to patient safety and comfort, as well as therapeutic effectiveness, must be solved before LEDs can by used in illuminators intended to be placed against the skin of a patient. Novel means of utilizing LEDs and similar intense light sources must be found before phototherapy safely effectively can be conducted at close range using such light sources for illumination. Such means must not materially increase the thickness, weight, or rigidity of a flexible illuminator, and must control heat and light output as necessary. There remains a need for a phototherapy illuminator which delivers a higher intensity of therapeutic light than current fiber-optic illuminators, while retaining the advantages of a flexible light-emitting mat and being safe and comfortable in use. These and other needs are met by the present invention, as is more fully discussed below.